1. Field of the Invention
The present invention relates to elastic wave devices, for example, bandpass filters and the like, and the present invention also relates to elastic wave modules.
2. Description of the Related Art
Elastic wave devices have been used as bandpass filters of cellular phones and the like.
Japanese Unexamined Patent Application Publication No. 2008-546207 describes one example of such elastic wave devices. The elastic wave device of the Japanese Unexamined Patent Application Publication No. 2008-546207 includes two elastic wave elements. In each elastic wave element, an interdigital transducer (IDT) electrode is located on one of principal surfaces of a piezoelectric substrate. The forgoing two elastic wave elements are joined with a middle layer therebetween in such a way that the principal surfaces of the piezoelectric substrates, on which their respective IDT electrodes are formed, face each other. External connector terminals are located on an outside-facing principal surface of one of the piezoelectric substrates.
In an elastic wave device described in International Publication No. 2011/102049, two elastic wave elements are joined, as in Japanese Unexamined Patent Application Publication No. 2008-546207 . In the International Publication No. 2011/102049, the thicknesses of piezoelectric substrates of the elastic wave elements are different from one another. External connector terminals are located on an outside-facing principal surface of the thinner piezoelectric substrate.
In Japanese Unexamined Patent Application Publication No. 2008-546207 and International Publication No. 2011/102049, however, the piezoelectric substrates are joined with the middle layer therebetween. This increases the distance between the external connection terminal and the elastic wave element on which no external connector terminal is formed. Thus, the foregoing elastic wave element has a large ground impedance. Accordingly, it is difficult to achieve a sufficiently large out-of-band attenuation in the elastic wave device.